The present invention relates to an anticorrosive structure of a fuel cell stack, and more particularly to an improvement technology providing for the increase in corrosion resistance and the reduction of cost of metal separators or terminal plates.
Solid polymer fuel cell stacks have a stack structure constituted by stacking the prescribed number of unit cells in which an anode and a cathode are disposed opposite each other on both surfaces of a solid polymer electrolyte membrane and the outer sides thereof are sandwiched by a pair of separators. When metal separators such as stainless steel separators are used, the metal should be corroded or dissolved in a long-term use, because the metal separators are exposed to corrosive atmosphere at a high temperature. If the metal separators are corroded, the eluted metal ions diffuse into the solid polymer electrolyte membrane and trapped in the ion exchange sites, thereby decreasing the ion conductivity of the solid polymer electrolyte membrane itself. Other consequences include the leak of reaction gases through holes which was formed in the metal separators by corrosion and the leak of coolant caused by erosion of seal lines. In order to avoid those problems, Japanese Patent Laid-open Publication No 2000-21418 suggested a method for surface treating (plating) the conductive separator with a metal layer, for example, a layer of gold or silver, that is inactive in an oxidizing atmosphere.
Furthermore, solid polymer fuel cell stacks have a stack structure constituted by stacking the prescribed number of unit cells in which an anode and a cathode are disposed opposite each other on both surfaces of a solid polymer electrolyte membrane and the outer sides thereof are sandwiched by a pair of separators, and a pair of terminal plates for taking out the power are disposed on both ends of the stack. Because an oxidation current flows in the terminal plate on the plus side, the terminal plate might be corroded if humid gas or coolant comes into contact therewith. Stack structures of various types have been studied with the object of increasing the corrosion resistance of terminal plates. For example, Japanese Patent Laid-open Publication No. 2003-163026 suggested a stack structure in which the terminal plate is prevented from coming into direct contact with humid gases or coolant by using a configuration in which a resin serving as an end plate material is fitted and inserted into a coolant channel of the terminal plate.
However, if all the metal separators constituting a fuel cell stack are surface treated with a noble metal such as gold or silver, the production cost rises.
Furthermore, in the stack structure described in Japanese Patent Laid-open Publication No. 2003-163026, a configuration is employed in which coolant channels pass through the terminal plates on both the plus side and the minus side. Therefore, both terminal plates have to be protected from corrosion and the production cost increases.